Here, for what it
is worth is a view of the inside of my aoogah horn. Sorry
that I did not take pictures while I had it apart for
painting. You are looking right in the hole in the front
of the horn.

I only took mine apart to clean and paint
the outside. I could have adjusted it without taking it
apart.

For the un-knowing, or un-caring, here is what I
SHOULD have taken pictures of. The front and the back are
held together with little bolts. The back is a plain old
motor, and on the end of the shaft is a wheel, about the
size of a 50 cent piece, with little V shaped bumps on
the side away from the motor -- facing what would be the
front of the car. There is a flat metal disk (A) sandwiched
between two gaskets that is held between the front and
the back of the horn. The gaskets crumbled when I took
the horn apart, but I fashioned new ones from sheet
gasket material from the local car supply store.

What is happening is that the nut (C) serves as a
lock nut, and the slotted screw (B)
goes through the flat disc and has a pokey end on the
back side. That screw adjusts the pokey end further or
closer to the bumps on the wheel. So, as you hit the
horn, the motor spins, rasping the V bumps against the
pokey screw (B)
and rattling the flat plate (A)
to make the raspy sound. If the pokey screw goes in too
far, it will strain the motor, or cause it not to spin at
all. If it is too loose, the motor spins and the V bumps
never even touch the screw, so no sound except a whirring
of the motor. Trial and error will get the loudest sound.

It was a bit tricky loosening the nut, and then
adjusting the depth of the screw, and then tightening the
nut to hold it in place. Short of taking it all apart and
cleaning everything up, a shot of WD-40 might help. I
used a long neck socket to loosen the holding nut,
adjusted with a long screwdriver, and then TRIED to
tighen the nut again. The screw wanted to move along with
the set nut. No real solution there, other than to design
a special long hollow socket that you can move while
holding the screw still with a screwdriver run down the
middle. MY solution was to over loosen the screw just the
right amount so that when both the screw and the nut
moved, they ended up in the right place. The nut must be
re-tightened though, or it will just vibrate looser and
looser.

Unbolt the front bellows from the horn and
remove it. At that point the gaskets and vibrating plate
will fall out. Reassemble the horn - the back, the
gasket, the vibrating plate, the other gasket -- but
leave off the bellows part. Then you can reach the
holding nut easily. Test the horn until you get the best
sound, tighten the holding nut, and then take it apart
again and reassemble WITH the bellows.